Symmetrical phthalocyanine bearing four triptycene moieties: Synthesis, photophysical and singlet oxygen generation

Abstract

Novel metal-free (7) and zinc(II) (8) phthalocyanine derivatives bearing four substituted triptycene moieties were synthesized and fully characterized by various spectroscopic methods including 'H-NMR, C-13-NMR, mass, FT-IR and UV-vis. Photophysical and photochemical properties such as electronic absorption, fluorescence emission, fluorescence lifetimes and singlet oxygen generation were investigated in toluene. The UV-vis spectra of 7 and 8 exhibited absorption bands in the visible region. The fluorescence lifetimes of 7 and 8 phthalocyanines were found to be 6.2 and 3.6 ns, respectively. The ability of the examined zinc(II) (8) and metal-free (7) to produce the singlet oxygen has been determined by both chemical and direct methods. While the chemical method 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen quencher was used in the first method, the direct determination has been done by recording the weak emission band of the singlet oxygen in the near-infrared region (1270 nm). From the direct process, the quantum yields of the singlet oxygen were found to be 0.28 (for 7) and 0.60 (for 8) and similar values were also obtained by the chemical method. The fluorescence quenching behavior of the studied phthalocyanine compounds (8 and 7) by electron-accepting 1,4 benzoquinone (BQ) was also studied in toluene. The powerful nanosecond laser flash photolysis technique was also employed to record the transient absorption spectra of the long-lived triplet states of the investigated compounds.